1. Field of the Invention
The present invention relates to an on-board type power supply module for a distributed power supply system and an electronic apparatus using the same, and more particularly a power supply module for improving power supply efficiency and an electronic apparatus.
2. Description of the Related Arts
With increasing complexity of an electronic apparatus such as an information processing unit, the electronic-apparatus is required to have improved reliability. As a distributed configuration is preferably applied to the electronic apparatus to obtain improved reliability, a power supply unit having a distributed configuration is also desired for the electronic apparatus. A distributed power supply system is currently applied for a server, a storage system, etc. The distributed power supply system requires a miniaturized power supply module which can be on-board mounted on a board for electronic units installed in the server, the storage unit, etc.
FIG. 9 is a configuration diagram of a prior art transformer-coupled switching power supply circuit. A primary winding 100 and two secondary windings 110, 120 are wound around a core of a transformer T, enabling transformer coupling between the primary side and the secondary side. The primary side is provided with an FET 102, which is a primary side circuit for controlling the current flowing through the primary winding 100, and a switching control circuit 104.
Meanwhile, on the secondary side, there are provided: pairs of FETs 114, 116 and 124, 126 respectively constituting rectifier circuits which rectify the current flowing through the secondary windings 110, 120; switching control circuits 112, 122; choke coils L1, L3 and capacitors C1, C2 which constitute smoothing circuits.
As is well known, in this switching power supply, switching control circuits 112, 122 controls to switch FETs 114, 116, 124, 126 to perform rectification operation of the secondary output, and to protect from overcurrent and overvoltage. Also, switching control circuit 104 controls FET 102 to protect from overcurrent on the primary side.
In such a way, when a large electric current is required on the secondary side, two secondary circuits are provided, constituting a so-called double-current configuration.
FIG. 10 is an explanatory winding diagram in a conventional power supply module, and FIG. 11 is an exploded configuration diagram of the conventional power supply module. As can be seen from FIGS. 10, 11, there are limits of a card size, component layout, etc. when miniaturizing the power supply module. A typical power supply module is structured of five layers L1–L5.
A top surface layer L1 and a bottom surface layer L5 are component-mounting layers, while inner layers L2–L4 are provided for forming circuit patterns. The top surface layer L1 is provided an one part of a transformer T, a primary winding 100 and primary-side circuit 102, 104, FETs 114, 116, 124, 126 of the secondary side circuit, one portion of switching control circuit 112, 122 on the secondary side, one input terminal 150 and one output terminal 160.
The bottom surface layer L5 is provided another part of the transformer T, the primary winding 100 and the primary-side circuit, choke coils L1, L3 and capacitor C disposed in the secondary side circuit, the other portion of the switching control circuit 112, 122 on the secondary side, another input terminal 152 and another output terminal 162.
A first inner layer L2 is provided two secondary windings 110, 120, a wiring area 132 for the primary side circuits 102, 104 and a wiring area 130 for the secondary switching control circuits 112, 122. A second inner layer L3 is provided a pair of output pattern films P1, P3, a wiring area 136 for the primary side circuits 102, 104 and a wiring area 138 for switching control circuits 112, 122 on the secondary side. A third inner layer L4 is provided a pair of ground films G1, G3, a wiring area 138 for the primary side circuits 102, 104 and a wiring area 140 for switching control circuits 112, 122 on the secondary side.
As shown in FIG. 10, the primary winding 100, the transformer T, and the pair of the secondary windings 110, 120 are disposed on a module, from left to right on this order. Together with these components, the primary side circuits 102, 104, the secondary side circuits 114, 116, 124, 126, and L1, L3, the output pattern films P1, P3 and the ground films G1, G3 are provided.
More specifically, the pair of secondary windings 110, 120 is drawn out in the same direction. Also, the secondary side circuits 114, 116, 124, 126, and L1, L3, the output pattern films P1, P3 and the ground films G1, G3 are disposed in such a manner that each point p1, u1, q1, s1, t1, p2, u2, q2, s2, and t2 in the secondary side circuit shown in FIG. 9 may be connected between the relevant layers through vias.
Now, in recent years, a load to which power is supplied from such a power supply module requires a large electric current. For example, a high-speed CPU requires larger current than a low-speed CPU. When. outputting such large current, the resistance and inductance included in the patterns of the power supply module become hardly negligible, because a large power loss and noise may be produced.
According to the above-mentioned layout of the conventional power supply module, the pair of secondary windings 110, 120 is drawn out in single direction, as illustrated in FIG. 10. Therefore, it is difficult to obtain large cross-section areas S of the secondary windings 110, 120. Also, in order to draw in single direction, it is necessary to mount both a pair of rectifier circuits and a pair of smoothing circuits of the secondary side on single side of the transformer T. To enable via connection with these secondary side circuits, the lengths l of the secondary windings 110, 120 have to be large.
The resistance r of the secondary windings is defined as r=ρ*l/S, the resistance value of the secondary windings cannot be small enough when l is large. Further, because the drawing of single direction requires a pair of output pattern films and a pair of ground films to be disposed on single side of the transformer T, it is difficult to have wide output pattern films and wide ground films. Therefore, it is difficult to reduce the output resistance.
As a result, when a large current is output, a large power loss is produced, and power supply efficiency is reduced. Further, because of large pattern lengths of the secondary windings, the inductance L becomes large. In the switching power supply, sharp current variation (di/dt) is produced by the choke coil and the transformer, the produced noise is determined as L*di/dt. Accordingly, when the current becomes large, the noise produced becomes hardly negligible, and a large switching noise is produced.
Needless to say, if a size of the power supply module may be large, the resistance value and the inductance of each pattern disposed on the pattern layers L2, L3, L4 can be smaller. However, the power supply module of large size does not fit for an apparatus in which miniaturization is desired.